The present invention relates to a method and an apparatus for polishing substrates such as semiconductor wafers.
FIGS. 1(a)-1(c) show a typical example of a process of fabricating an interconnect or wiring circuit on a semiconductor substrate W. In FIG. 1(a), the semiconductor substrate W comprises a base layer 101, an electrically conductive layer 101a, a SiO2 insulating layer 102 in which a contact hole 103 and a groove 104 forming a circuit wiring or interconnect pattern have been formed by lithograph-etching, a barrier layer 105 made of TiN or the like, and a seed layer 107. The semiconductor substrate W is, as shown in FIG. 1(b), plated with metal having a high electrical conductivity, in this example copper, so that a copper layer is formed over the substrate W with the contact 103 hole and the groove 104 being filled with the copper 106. The semiconductor substrate is thereafter subjected to chemical-mechanical polishing to remove the copper layer together with the seed layer 107 and the barrier layer 105 on the surface of the insulating layer 102, leaving the copper 106 in the contact hole 103 and the groove 104 in such a manner that the outer surface of the copper 106 in the hole 103 and the groove 104 is flush with the surface of the insulating layer 102, whereby the copper 106 forms a circuit wiring or interconnect of the substrate.
It is necessary for the polishing process mentioned above to be conducted through several steps in which different polishing conditions are respectively set since the polishing is conducted on a plurality of layers formed on the insulating layer 102 including the copper layer, the seed layer and the barrier layer. In a conventional polishing apparatus, there are provided a plurality of polishing tables suitable for those polishing steps. Accordingly, the conventional polishing apparatus is large, complex in construction, expensive and inefficient or of low throughput.
Further, in a polishing operation of the prior art, a substrate carrier brines the entire surface of a substrate to be polished into contact with the polishing surface of the turntable at a position spaced away from the center of the polishing surface in order to increase the polishing speed. Thus, the polishing surface of the turntable is required to have a large diameter. For example, to polish a substrate having a diameter of 200 mm, the polishing surface is required to have a diameter of about 600 mm. Furthermore, if it is required to make a real-time measurement of a thickness of a surface layer of a substrate which is being polished, a special arrangement of a thickness measuring device (for example, embedding a thickness measuring device into a turntable) must be prepared.
In the light of the above, the present invention aims to provide a polishing apparatus and a method which enable layers of a substrate to be polished with a single-turntable having a small diameter while conducting a real-time thickness measurement of the layers which are being subjected to polishing, thereby solving the problems involved in the prior art such as low throughput, complexity and size of the polishing apparatus.
In accordance with the present invention, there is provided a method of polishing a substrate comprising: bringing a surface of a substrate to be polished into contact with a polishing surface of a polishing table in such a manner that a portion of the surface of the substrate extends outwardly from an outer periphery of the polishing surface; rotating the substrate about its center axis while keeping the surface of the substrate in contact with the polishing surface of the polishing table; and controlling an attitude of the substrate which is being rotated.
The method may further comprise measuring a thickness of a surface layer of the substrate on the basis of measurement of the thickness of the surface layer of a portion of the substrate extending outwardly from the periphery of the polishing surface while the substrate is being rotated.
The method may furthermore comprises supplying a polishing liquid between the surface of the substrate and the polishing surface of the polishing table, wherein substrate polishing conditions are changed in response to the progress of the polishing of the surface of the substrate by changing a force for urging the surface of the substrate against the polishing surface, a number of revolutions per minute of the substrate, a number of revolutions per minute of the polishing table and/or a kind of the polishing liquid. It is preferable that when the polishing liquid is changed from a certain kind of polishing liquid to another kind of polishing liquid, the polishing surface of the polishing table is subjected to a cleaning operation to remove residue of the polishing liquid used in the preceding steps of the polishing of the surface of the substrate to avoid the production of an undesired compound.
In accordance with another aspect of the present invention, there is provided an apparatus for polishing a substrate comprising: a polishing table having a polishing surface; a substrate carrier for holding a substrate and bringing it into contact with the polishing surface in such a manner that a surface of the substrate to be polished is brought into contact with the polishing surface of the polishing table, with a portion of the surface of the substrate extending outwardly from the outer periphery of the polishing surface; and an attitude controller for controlling an attitude of the substrate carrier to keep the surface of the substrate parallel with the polishing surface of the polishing table.
The apparatus may comprise a layer thickness measuring device for determining a thickness of a surface layer of the substrate by measuring the surface layer of the portion of the substrate extending outwardly from the outer periphery of the polishing surface of the polishing table.
Specifically, the apparatus further comprises: a rotatable drive shaft and a universal joint drivingly connecting the drive shaft to the substrate carrier so that the universal joint transmits rotation of the rotatable drive shaft to the substrate carrier while allowing the substrate carrier to tilt relative to the drive shaft. The attitude controller controls the attitude of the substrate carrier by controlling an angle of tilt of the substrate carrier relative to the drive shaft. The attitude controller may comprise a stationary electromagnetic device and an armature securely provided on the substrate carrier so that the armature is moved by means of electromagnetic force generated by the stationary electromagnetic device, whereby the attitude of the substrate carrier is controlled.
According to a further aspect of the present invention, there is provided a method of polishing a substrate comprising: bringing an entire area of a surface of a substrate to be polished into contact with a polishing surface of a polishing table; causing relative movement between the surface of the substrate and the polishing surface while keeping the surface of the substrate in contact with the polishing surface to polish the surface of the substrate; shifting the substrate relative to the polishing surface while keeping the surface of the substrate in contact with the polishing surface so that the surface of the substrate partly extends outwardly from the outer periphery of the polishing surface; and measuring a thickness of a surface layer of the substrate on the basis of measurement of the thickness of the surface layer of a portion of the substrate extending outwardly from the periphery of the polishing surface.
According to another aspect of the present invention, there is provided an apparatus for polishing substrates comprising: a polishing table having a polishing surface; a substrate carrier for holding a substrate, the substrate carrier being movable between a polishing position in which an entire area of a surface of a substrate to be polished is brought into contact with the polishing surface and a measurement position in which the surface of the substrate partly extends outwardly from the outer periphery of the polishing surface; and a layer thickness measuring device for determining a thickness of a surface layer of the substrate by measuring the surface layer of the portion of the substrate extending outwardly from the outer periphery of the polishing surface of the polishing table. Further, the present invention provides an apparatus for polishing substrates comprising a polishing table having a polishing surface and a transparent ring positioned outside and fixedly connected to an outer peripheral edge of the polishing surface, the transparent ring having a flat surface which is flush with the polishing surface of the polishing table. The apparatus may comprise a layer thickness measuring device disposed under the transparent ring for measuring thickness of a surface layer of the substrate. Furthermore, the apparatus comprises a substrate carrier for holding the substrate, the substrate carrier being movable between a polishing position in which an entire area of a surface of a substrate to be polished is brought into contact with the polishing surface and a measurement position in which the surface of the substrate partly extends outwardly from the outer periphery of the polishing surface. The transparent ring may be replaced by a stationary transparent member positioned outside, spaced away from and adjacent to an outer peripheral edge of the polishing surface. The stationary transparent member has a flat surface which is flush with the polishing surface of the polishing table.
Preferred embodiments of the present invention will now be described in detail with reference to the attached drawings.